Checkout Fails Avatax And Sucuri Firewall

We use a third-party sales tax service called Avalara and their AvaTax service. Once a customer enters their shipping info in checkout the add-on connects behind the scenes to get the sales tax rate and the sales tax amount and puts it into the tax value in the cart.

This has been working fine for 3 years.

We recently had no sales for several days. Checked and found lots of abandoned carts. Decided to do test purchase. We get an error that it couldn't connect to the sales tax provider host.

The add-on has a test connection button and we get same connection failed message.

We recently added Sucuri firewall to our GoDaddy hosting (I know, I know). As part of the set up we had to whitelist multiple internal script path files and external URLs for fonts and such. We did whitelist the 3 URLs for the Avatax calculation service but still not working. Any ideas?

Maybe it has something to do with the HTTP/1 and HTTP/2 protocol which a lot of us were having issues with recently?

Thanks Tool. That was a very good idea even though it did not fix my issue.

I disabled the firewall but that did not fix it. So, not the firewall. From what I can see in the Console > Network it isn't sending out the request to the external service. Either that, or I'm not understanding the console detail.

I've also downloaded the add-on and diff'd the files against what is in the store and they are all the same with one exception. The

avatax_tax_calculation > AvaTax4PHP > classes CancelTaxResult.class.php

is very different. I'm thinking I could replace the file and test it. Just hate to go off on troubleshooting tangents.

Check the http request logs in admin panel and see if the request/response to avatax shows any errors.